臺灣博碩士論文加值系統

颱洪期間所帶來的超高流量經常導致橋梁等跨河構造物結構破壞和功能失效。在眾多洪水衍生的橋樑破壞案例中，橋墩基礎周邊的局部沖刷被認為是致災的關鍵因素之一。以水理機制而言，墩柱迎水面的向下射流與近床區域的馬蹄形渦流為局部沖刷的主要驅動力。為因應此一問題，本研究提出了一種靈感來自鯊魚鱗片的微型仿生結構「鱗齒」，用以安裝於橋墩表面來降低墩柱前向下射流的強度，進而減弱或消除馬蹄形渦流來減緩局部沖刷。相較於其他大型的橋墩保護工，仿鱗齒結構長度僅需橋墩直徑的0.25倍，寬度為橋墩直徑的0.4倍即可發揮保護效力。
為量化仿鱗齒結構對橔柱周圍流場之影響，本研究透過粒子追蹤測速法量測三種不同圓柱之瞬時流場，分別為平滑圓柱流場、鱗齒圓柱流場與逆鱗齒圓柱流場。鱗齒與逆鱗齒之分別僅在於安裝方向的不同而沒有結構設計之差異。基於所測得的瞬時流場，本研究分析了向下射流、渦度、漩度、紊流動能、雷諾剪應力、等水理特性，並利用正交特徵分解法進一步解構出具有高能量貢獻度之低模態紊流結構。
透過比較三種不同圓柱流場之差異，本研究指出鱗齒結構能有效降低向下射流強度約80%，達到抑制馬蹄形渦流生成之效果。此外，鱗齒結構亦分別減弱了柱前紊流強度及雷諾剪應力約達45%及35%，有效穩定流況並降低水流對底床泥沙的作用力。在渦度和漩度的觀測上，鱗齒圓柱可在鱗齒結構下側產生逆時針渦漩。在正交特徵分解法的前三模態中，紊流動能亦僅分布在鱗齒結構下方而非柱前的底床表面，顯示鱗齒能有效降低水流對底床泥沙的擾動程度。經額外動床試驗證實，鱗齒確實可降低柱前局部沖刷深度約22%。綜合而言，鱗齒相較於其他的防沖刷策略更具有工程經濟性、施工方便性和實用性等優勢。

During typhoon and flood events, the excessive flow often leads to structural damage and functional failure of river-crossing structures like bridges. Among the nu-merous bridge failures caused by flooding, local scour around bridge piers is consid-ered one of the key contributing factors. From a hydraulic mechanism perspective, the downward flow on the upstream face of the pier and the horseshoe vortex near the bed are the main drivers of local scour.
To quantify the impact of the bio-inspired denticles on the flow field around the pier, this study employed Particle Tracking Velocimetry (PTV) to measure the instan-taneous flow fields of three different cylindrical models: a smooth cylinder, a denticle cylinder, and a reverse denticle cylinder. The difference between the denticles and the reverse denticles lies only in the installation direction, with no difference in structural design. Based on the measured instantaneous flow fields, this study analyzed various hydraulic characteristics such as downward flow, vorticity, swirling strength, turbulent kinetic energy, Reynolds shear stress, and more. Additionally, the study used Proper Orthogonal Decomposition (POD) to further decompose the low-order turbulent struc-tures with high energy contributions.
By comparing the differences in the flow fields of the three cylindrical models, this study found that the denticle structure effectively reduces the intensity of the downward flow by about 80%, achieving the effect of suppressing the formation of the horseshoe vortex. Moreover, the denticle structure also reduced the turbulence intensity in front of the pier by about 45% and the Reynolds shear stress in front of the pier by about 35%, effectively stabilizing the flow condition and reducing the impact of the flow on the bed sediment.
Observations of vorticity and swirling strength showed that the denticle structure only generated counterclockwise vortices on the underside of the structure, inhibiting the possibility of downward scour. In the first three modes of the POD method, the en-ergy distribution of the denticle structure was all located below the structure, effective-ly stabilizing the flow's impact on the bed sediment. In additional mobile bed experi-ments, the denticles reduced the local scour depth by approximately 22%. Based on the comprehensive analysis, this structure exhibits advantages such as engineering econo-my, ease of construction, and practicality among various scour protection strategies.

摘要 i
ABSTRACT ii
目錄 iii
圖目錄 v
表目錄 viii
符號說明 ix
第一章 緒論 1
1.1 前言 1
1.2 研究動機與目的 5
1.3 文章架構 6
第二章 文獻回顧 7
2.1 垂直圓柱周圍流場結構 7
2.2 紊流條件下馬蹄形渦流的形成位置 9
2.3 馬蹄形渦流中TKE與RSS的特徵分析 12
第三章 實驗設置與步驟 16
3.1 定床實驗水槽設置與配置 16
3.1.1 定床實驗水槽 16
3.1.2 仿鱗齒裝置 17
3.1.3 粒子追蹤測速實驗設計 20
3.1.4 定床實驗條件 21
3.2 定床實驗儀器介紹 24
3.3 定床實驗步驟 29
3.4 動床實驗設置 30
3.5 動床實驗步驟 32
第四章 分析方法 33
4.1 Particle Tracking Velocimetry (PTV) Method 33
4.1.1 影像預處理和粒子識別 33
4.1.2 粒子匹配 34
4.2 正交分解方法(POD) Proper Orthogonal Decomposition 37
4.3 雷諾剪切應力(RSS) Reynolds Shear Stress 39
4.4 紊流動能傳輸方程式 (Turbulent Kinetic Energy Transport Equation) 42
4.5 渦度(Vorticity)與渦漩強度(Swirling strength) 44
第五章 實驗結果與討論 46
5.1 向下射流 46
5.2 瞬時流場與流線分佈變化 50
5.3 渦度(Vorticity)與渦漩強度(Swirling strength) 55
5.4 紊流動能(TKE) Turbulent Kinetic Energy 57
5.5 紊流動能傳輸方程式 (Turbulent Kinetic Energy Transport Equation) 63
5.6 雷諾剪切應力(RSS) Reynolds Shear Stress 68
5.7 象限分析 Quadrant Analysis 73
5.8 正交分解方法(POD) 77
5.9 鱗齒裝置安裝位置分析 81
5.10 動床沖刷實驗分析 85
第六章 結論與相關建議 87
6.1 三種不同圓柱模型比較分析 87
6.2 鱗齒裝置於不同深度位置比較分析 87
6.3 動床循環渠道 88
6.4 建議 88
參考文獻 89

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